Bill Belichick's defensive rebuilding project just became bigger with Ty Warren sidelined for the season by a hip injury.

The New England Patriots placed the defensive end on injured reserve Friday after he missed most training-camp practices and Thursday night's 27-24 preseason-opening victory over the New Orleans Saints.

Warren, who was hurt during the third practice of training camp, told Comcast SportsNet New England that he decided to have the surgery after "laboring around for about a year-and-a-half" on the hip.

"It was something that I wanted to get done. That I needed to get done," Warren said. " ... The season's too long to be taking shots all year, to feel OK one week and feel bad the next. To have arthritis and not be able to be me. I'm going to sacrifice one year for the next couple."

Warren, 29, has two years remaining on his contract with the Patriots.

Dr. Mark Philippon, a hip specialist who also worked on Miami Dolphins wide receiver Brandon Marshall and New York Giants defensive end Osi Umenyiora, is scheduled to perform the surgery Monday in Vail, Colo. According to Comcast SportsNet New England, rehabilitation will take four to six months.

"Tough break, but we have to move on," Belichick said of Warren's injury. "He's missed quite a bit of time the last couple of years, so we've had to deal with that anyway. Unfortunately, that's part of the game. We'll just move ahead."

Fortunately for the coach, linebacker Derrick Burgess reported Friday and was reinstated from the reserve-did not report list after considering retirement. Burgess gives the Patriots an outside pass rusher, somewhat mitigating the loss of Warren. Burgess passed his physical and conditioning test Friday and is expected to practice Sunday after Saturday's day off.

Burgess had 38 sacks in four seasons with the Oakland Raiders, then was traded to the Patriots before last season. He had five sacks with New England.

"Derrick is a very knowledgeable pass rusher," Belichick said. "I think he has a good understanding of his opponents, pass rush technique and how to defeat blockers. Derrick is really a pretty versatile player."

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Belichick is playing a bigger role in defensive planning after Dean Pees resigned as coordinator following last season and wasn't replaced. Pees now is linebackers coach of the Baltimore Ravens.

The Patriots' linebacking corps, retooled since Tedy Bruschi retired and Mike Vrabel was traded to the Kansas City Chiefs before last season, has plenty of young talent, led by 2008 NFL Defensive Rookie of the Year Jerod Mayo.

However, the depth of the defensive line could be a problem.

Last summer, the Patriots' top four linemen were nose tackle Vince Wilfork and ends Warren, Richard Seymour and Jarvis Green. Only Wilfork remains. Seymour was traded to the Raiders eight days before the Patriots' 2009 opener, and Green, who took Seymour's starting job, signed with the Denver Broncos during the offseason.

The Patriots still have Mike Wright, who's entering his sixth NFL season. Without Warren, veteran newcomers Damione Lewis and Gerard Warren should see more playing time, but both are adjusting from a 4-3 defense they played with their previous teams to the 3-4 alignment.

"Damione played in St. Louis and Carolina again, primarily as a three-technique, lining up on the guard's outside shoulder," Belichick said. "In a 3-4 defense, we really don't have that player.

"Like Gerard, he's played a lot of football. He's played against a lot of good players. He's a smart guy and a very experienced guy and he's been able to make the adjustments to our system and our style of play."

Gerard Warren played his first four seasons with the Cleveland Browns, then two with Denver and three with Oakland.

"He's shown a lot of improvement," Belichick said. "He did a lot of good things in (Thursday's) game. He played with good effort and he made a nice play with a screen pass down the field, for example, things like that. We know he is a strong, physical player on the line of scrimmage and he's shown good ability to rush the passer.

"(He) had a couple quarterback hurries and also he showed up well in pursuit. I think he's made the transition pretty well."

But Ty Warren was a reliable contributor ever since the Patriots drafted him from Texas A&M with the 13th pick of the 2003 draft. He started 92 of his 105 games in seven years and missed just one game in his first five seasons. Then he sat out three in 2008 with a groin injury and three more last year with an injured ankle.